88 Comp with low compression in one cylinder?

[supra88']

I'm pretty new to this forum and have got some GREAT info from you guys. I go to the lake at least 3 or 4 times a week and we do a lot of wakeboarding (even tho I'm not great cause im always stuck driving everyone else lol) and I have noticed the boat is starting to struggling a little more out of the hole shot. So yesterday I did a compression test on my 351w and all the cylinders were between 110-115, but one was 100 and another was only 70. I put a little oil in the 70 psi cylinder and checked it again and it did not come up very much, maybe 5psi... Looks like I have lost a cylinder and I know this is bad, but exactly how bad? Pretty sure a rebuilt is not too far in my future...

Thanks